Recently, we described new processes for making polyetherester resins from polyethers (see U.S. Pat. Nos. 5,319,006, 5,436,313, and 5,436,314, and U.S. application Ser. No. 08/619,059, filed Mar. 20, 1996). In each process, a polyether reacts with a cyclic anhydride, a dicarboxylic acid, or a diol diester in the presence of an "insertion" catalyst. The anhydride, dicarboxylic acid, or diol diester inserts randomly into carbon-oxygen bonds of the polyether to generate ester bonds in the resulting polyetherester resin. The polyetherester resin is then combined with a vinyl monomer, preferably styrene, and is cured to produce a polyetherester thermoset. Lewis acids, protic acids having a pKa less than about 0, and metal salts thereof are effective insertion catalysts. The insertion process provides a valuable and versatile way to make a many unique polyetherester intermediates.
More recently (see application Ser. No. 08/608,379, filed Feb. 28, 1996), we extended the insertion technology by developing a process for making high-performance polyetherester resins. These high-performance resins are made by chain extending a polyetherester resin (made by insertion) with a primary diol or a diepoxy compound. The high-performance resins give thermosets with improved high-temperature performance, better tensile and flex properties, and enhanced resistance to aqueous solutions--particularly aqueous acid and caustic solutions--compared with those made using the earlier polyetherester resins.
The polyester industry recognizes the problem of poor water resistance and inadequate tensile and flex properties of many commercial general-purpose polyester systems. In response, the industry has developed two classes of high-performance resins: isophthalate resins (hereinafter also called "iso resins") and vinyl esters. "Iso resins," which incorporate recurring units of isophthalic acid, give thermosets with better corrosion resistance compared with those made using general-purpose polyester resins. Because isophthalic acid is relatively expensive, however, and because processing can be time-consuming, iso resins provide better water resistance at a price. In addition, iso resins are still quite susceptible to degradation by aqueous caustic solutions.
Vinyl ester resins currently provide the highest level of physical properties available in the unsaturated polyester industry. When performance must be excellent, and low cost is not so important, vinyl esters are often used. Vinyl esters give thermosets with an excellent overall balance of properties, including high tensile and flex strengths and excellent corrosion resistance. Unfortunately, vinyl esters are by far the most expensive resins. In addition, vinyl ester resins are not easily thickened, and this limits their usefulness in SMC applications.
Another problem with the more expensive varieties of resins now available is that they are often incompatible with less expensive resins. For example, vinyl ester resins are not generally compatible with general-purpose resins. Thus, blending offers no value to a formulator who might wish to boost physical properties of a general-purpose resin by blending in vinyl ester, or to cheapen a vinyl ester formulation by adding some general-purpose resin.
Resin blends that can improve thermoset properties and/or reduce costs are needed. The excellent physical properties, low cost, and unique structure of epoxy-extended polyetherester resins prompted us to investigate blends of these resins with commercial polyester resins.